Re: [PATCH kmod 09/13] libkmod: swap alloca usage for a few assert_cc

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On Tue, Apr 30, 2024 at 07:47:46PM GMT, Emil Velikov wrote:
On Tue, 30 Apr 2024 at 19:43, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote:

On Tue, Apr 30, 2024 at 07:27:00PM GMT, Emil Velikov wrote:
>On Tue, 30 Apr 2024 at 19:18, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote:
>>
>> On Tue, Apr 30, 2024 at 06:54:00PM GMT, Emil Velikov wrote:
>> >On Tue, 30 Apr 2024 at 18:39, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote:
>> >>
>> >> On Mon, Feb 12, 2024 at 05:23:10PM GMT, Emil Velikov via B4 Relay wrote:
>> >> >From: Emil Velikov <emil.l.velikov@xxxxxxxxx>
>> >> >
>> >> >Since all the compression magic is always available now, we don't need
>> >> >to loop at runtime nor use alloca - latter of which comes with a handful
>> >> >of caveats.
>> >> >
>> >> >Simply throw in a few assert_cc(), which will trigger at build-time.
>> >> >
>> >> >Signed-off-by: Emil Velikov <emil.l.velikov@xxxxxxxxx>
>> >> >---
>> >> > libkmod/libkmod-file.c | 22 ++++++++--------------
>> >> > 1 file changed, 8 insertions(+), 14 deletions(-)
>> >> >
>> >> >diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
>> >> >index b69f1ef..5b88d6c 100644
>> >> >--- a/libkmod/libkmod-file.c
>> >> >+++ b/libkmod/libkmod-file.c
>> >> >@@ -410,7 +410,6 @@ struct kmod_file *kmod_file_open(const struct kmod_ctx *ctx,
>> >> > {
>> >> >       struct kmod_file *file = calloc(1, sizeof(struct kmod_file));
>> >> >       const struct comp_type *itr;
>> >> >-      size_t magic_size_max = 0;
>> >> >       int err = 0;
>> >> >
>> >> >       if (file == NULL)
>> >> >@@ -422,22 +421,17 @@ struct kmod_file *kmod_file_open(const struct kmod_ctx *ctx,
>> >> >               goto error;
>> >> >       }
>> >> >
>> >> >-      for (itr = comp_types; itr->load != NULL; itr++) {
>> >> >-              if (magic_size_max < itr->magic_size)
>> >> >-                      magic_size_max = itr->magic_size;
>> >> >-      }
>> >> >-
>> >> >-      if (magic_size_max > 0) {
>> >> >-              char *buf = alloca(magic_size_max + 1);
>> >> >+      {
>> >> >+              char buf[7];
>> >> >               ssize_t sz;
>> >> >
>> >> >-              if (buf == NULL) {
>> >> >-                      err = -errno;
>> >> >-                      goto error;
>> >> >-              }
>> >> >-              sz = read_str_safe(file->fd, buf, magic_size_max + 1);
>> >> >+              assert_cc(sizeof(magic_zstd) < sizeof(buf));
>> >> >+              assert_cc(sizeof(magic_xz) < sizeof(buf));
>> >> >+              assert_cc(sizeof(magic_zlib) < sizeof(buf));
>> >>
>> >> ../libkmod/libkmod-file.c: In function 'kmod_file_open':
>> >> ../shared/macro.h:25:9: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
>> >
>> >Is there a particular use-case for explicitly forcing C90?
>>
>> not forcing C90, but forcing -Wdeclaration-after-statement as per
>> flag passed in configure.ac. I think the message given by gcc is
>> misleading here.
>>
>
>Indeed thanks. Seems like I should add `export CFLAGS+=-Werror" to my dev box.

so, are you ok that I just squash this?


Yes, of course.

thanks, pushed everything except the last patch.

Lucas De Marchi


-Emil




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